The present invention is directed to bicycle derailleurs and, more specifically, to a bicycle derailleur having links pivotably mounted to a base member and a movable member through pivot pins where bearings are disposed at selected ones of the pivot pins.
FIG. 1 is a conceptual drawing of a conventional bicycle derailleur 10. Derailleur 10 includes a base member 14, a movable member 18, and links 22 and 24 coupling movable member 18 to base member 14 so that movable member 18 is capable of movement relative to base member 14. Base member 14 ordinarily is fixed to a bicycle frame (not shown), and movable member 18 ordinarily supports a chain guide (not shown) for moving a chain across a plurality of sprockets (not shown). Link 22 is pivotably coupled to base member 14 through a pivot pin 28 and to movable member 18 through a pivot pin 32. Similarly, link 24 is pivotably coupled to base member 14 through a pivot pin 36 and to movable member 18 through a pivot pin 40. Base member 14, movable member 18 and links 22 and 24 thus form a four-bar type linkage mechanism which, in this case, is in the form of a parallelogram. A bias spring 44 may be connected between diagonal corners of the linkage mechanism formed by base member 14, movable member 18 and links 22 and 24 to create a biasing force F.sub.B which biases movable member 18 in a desired direction. In FIG. 1, base member 14 is stationary, so movable member 18 is biased upward when bias spring 44 is connected as shown.
Since bias spring 44 is connected between diagonal comers of the linkage mechanism, substantial spring force is applied to all four pivot points located at pivot pins 28, 32, 36 and 40, thus creating enhanced friction at each pivot pin. To compensate for such friction, a bearing 50 is mounted around pivot pin 28 between pivot pin 28 and link 22, a bearing 54 is mounted around pivot pin 32 between pivot pin 32 and link 22, a bearing 58 is mounted around pivot pin 36 between pivot pin 36 and link 24, and a bearing 62 is mounted around pivot pin 40 between pivot pin 40 and link 24. While bearings 50, 54, 58 and 62 help to overcome the friction between pivot pins 28, 32, 36 and 40 and links 22 and 24, the bearings make the cost of the derailleur much greater.